Pressurized degasification of crude oil by sonic wave action



Oct. 6, 1964 A. cs. BODINE 3,151,953

PRESSURIZED DEGASIFICATION OF CRUDE OIL BY SONIC WAVE ACTION Filed Aug. 26, 1957 2 Sheets-Sheet 1 FIG.|

INVENTOR. ALBERT G. BODlNE ATTORNEY Oct. 1964 A. s. BODINE 3,151,958

PRESSURIZED DEGASIFICATION 0F CRUDE OIL BY SONIC WAVE ACTION Filed Aug. 26, 1957 2 Sheets-Sheet 2 FIG. 3

INVENTOR.

ALBERT G. BODJNE ATTORNEY United States Patent 3,151,?58 PRESSUREZEE DEGASTFTQATTQN 0F CRUBE GE BY SQNEC WAVE ACTHIN Albert G. Bodine, 7877 Woodley Ava, Van Nuys, Calif. Filed Aug. 26, 1957, Ser. No. 68%,138 1 iClairn. {61. 55-45) This invention relates generally to the separation of gas from crude oil, and more particularly to methods for degassing or fractionating crude oil as it comes from the well under super-atmospheric pressure, without losing gas pressure. The invention may be practiced in the oil field near the well head, and furnishes a means by which gas or light fractions may be removed from the crude without pressure depletion, and therefore without making necessary recompression for purpose of transportation through the pipe lines. The invention is to be distinguished from known processes involving fractionization in the vapor phase, as well as processes for degassing liquids at substantially atmospheric pressure.

Crude oil from the Well is now normally passed through a pressure reducing system, sometimes called a trap farm, where the reduction in pressure causes the gaseous hydrocarbons to boil out of the crude. In its natural occurrence in the earthen reservoir, the crude oil has a large amount of dissolved gas, increasing in amount with increased pressure. A large portion of this dissolved gas can be and is generally removed by simply reducing the pressure, allowing the crude to blow down as it passes through the transmission system leading from the well.

This blowing down of the crude is a very wasteful process, because a great amount of energy is lost as the gas is permitted to expand to a large volume. This large volume of low-pressure gas is then generally drawn from the tops of the trap-farm tanks and subsequently compressed by large and expensive centrally located compressor plants so as to repressurize the gas sufiiciently that it can be transmitted through economically sized pipe lines. The compressor plants are thus needed to replace a a-rge amount of compression energy which was wasted when the gas was blown down in order to be released from the crude. These compressor plants and the piping required therewith, are very expensive installations.

A primary object of the present invention is accordingly the provision of a novel method for separatirig the gas from the crude oil without blow-down, so as to avoid the necessity of repressurization by compressor plants.

Also, the process of blow-down releases not only gas fractions desired to be released, but fractions such as butane and pentane ordinarily desired to remain in the crude. Therefore, it is now common to provide scrubbers or absorbers to reintroduce such fractions back into the crude.

A further object is accordingly to provide a gas separation process capable of difierentiatiag between light fractions desired to be released, and heavier fractions desired to be retained in the crude.

The present invention, broadly considered, consists in causing a release of dissolved gas from the crude under sonic wave action without depletion of over-all pressure. In carrying out the invention, a sonic wave is caused to act on the liquid crude while the latter is held within an elevated pressure system. This wave involves pressure amplitude fluctuations above and below van elevated mean pressure. Gas fractions apparently go rapidly out of solution under such conditions as the wave amplitude approaches or attains those corresponding to cavitation for the several fractions present. When cavitation occurs, low-pressure bubbles are cyclically formed, which fill with gas coming out of solution in the crude. It will be noted that the large pressure amplitude swing that would 3,151,958 Patented Oct. 6, E954 be required to cavitate the crude itself is not required. Each fraction present begins to go rapidly out of solution as the descending pressure amplitude approaches or attains cavitation amplitude for that fraction. The several gas fractions recoverable, such as methane, ethane, propane, etc., are commonly in a state of solubility equilibrium, such that a moderate pressure reduction may take them out of solution. A cyclic lowering of the pressure, in the range above the cavitation level, may drive a certain amount of gas out of solution, owing merely to dropping the pressure below the level at which the gas can stay in solution at its concentration in the crude. As the pressure is then dropped below the cavitation level, low pressure voids are formed, and fill with gas coming out of solution owing to the pressure drop. The gases come out of solution very rapidly with cavitation, or at pressure levels corresponding to cavitation conditions.

I may adjust the amplitude of my sonic Wave system to obtain the degree of degasifioation desired. Thus, with moderate amplitudes, the smaller molecule gases such as ethane and methane are released, as well as the gases present in large proportions. With higher Wave amplitudes, larger molecule gases tend to be released as well as those existing in minor percentages. Thus, I may, for example, set the sonic wave amplitude, in relation to mean pressure, such as to separate out methane, ethane and propane, and to leave in solution butane and pentane. A characteristic of the invention may be stated to be the fractionation of crude oil by sonic wave action at an elevated mean pressure, employing a pressure wave swing of an amplitude sufiicient to remove selected gas fractions, yet appreciably less than the mean pressure of the crude. A preferred embodiment of the invention is one in which a sonic standing wave is established in the crude. Gas separation and accumulation occurs primarily in the pressure antinode regions of the wave, and may be collected therefrom.

The separated gas is preferably continuously removed from the region of the crude in order to minimize its going back into solution. However, owing to gas saturation of the liquid interface of the gas bubbles, the sep arated gas does not tend to go rapidly back into solution.

The invention will be better understood from the following detailed description of certain present illustrative embodiments thereof, reference for this purpose being had to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view through illustrative apparatus in accordance with the invention;

FIG. 2 is a medial section through a modified form of the invention;

FIG. 3 is a longitudinal section of another embodiment of the invention;

FIG. 4 is a view taken on line 44 of FIG. 3; and

FIG. 5 is a view partly in elevation and partly in longitudinal section showing still another embodiment of the invention.

Referring first to that form of my invention shown in FIG. 1, numeral 19 designates a longitudinally curved sonic pipe, in this case generally semicircular in longitudinal curvature, with its two ends uppermost and its midsection horizontal and at the bottom. A crude oil intake pipe 11 feeds two branch pipes 12 which lead into sonic pipe 10 at points somewhat below the extremities thereof. A liquid discharge pipe 13 leads from the lowermost point of the midsection of pipe 10. The two ends of the pipe 16 are fitted with caps 14 and 15, from which extend gas discharge pipes 1e and 17, respectively. The pipe 16 is shown as including an optional check-valve device 18, comprising an enlarged chamber 19 having a conical top 29 and containing a float check-valve element 21 adapted to seat on the inside surface of the conical top. When liquid is not present within the chamber 19, the ball 21 rests on support lugs 22. The check-valve 13 will be seen to act upon rise of liquid level within chamber 19 to move float 21 against conical top 20 and thereby pre-. vent discharge of liquid therepast.

Inlet line 11 and discharge line 13 may be furnished with suitable control valves 11a and 13.1, respectively, as indicated. Normally, the rate of inflow and outflow are established such that the sonic pipe 19 is maintained substantially full of crude oil, up to its end caps 14 and 15.

A sonic standing wave is created and maintained in the sonic pipe 10, and for this purpose I have shown in FIG. 1 a horizontal cylinder 25 containing oscillating piston 26 driven by crank 27 from engine-driven eccentric 28, the end of the cylinder beyond the piston being coupled into one end of sonic pipe 163 by means of fitting 29. It will be noted that the orientation of the piston and the coupling to the pipe have been made such that a gas pocket cannot collect between the piston and the liquid in pipe 10. The stroke of the piston may be adjusted by use of interchangeable eccentrics 28 of different throws. Reciprocation of piston 26 in cylinder 25 launches alternating waves of compression and rarefaction in the col- 7 umn of liquid contained within the pipe 10. By operating the reciprocating piston 26 at a frequency corresponding to a resonant frequency of the sonic pipe 1% for longitudinal waves in the liquid medium thereof, a standing wave may be established in the liquid column within the pipe 10.

This standing wave may be of a half wavelength, having a velocity antinode V at the midpoint of the sonic column 10, and pressure antinodes P and P at the two extremities of the pipe. On each forward stroke of the pis ton 26 in its cylinder 25 a positive pressure pulse is launched in the liquid column in the system, and travels around the sonic pipe 10 to its far end, where it is reflected at the cap 14 and returned in the reverse direction to its point of origination at the beginning end of the pipe 10. The time taken for this round trip of compression wave is, of course, a function of the length of the pipe 10 and of the velocity of sound in the media through which the wave is traveling. To obtain resonance, the piston 26 is driven at such speed as to produce a second pressure pulse coincidentally with the return of the reflected pressure pulse, with the consequence that the pressure pulse amplitude is thereby augmented.

In between the pressure pulses so delivered by the piston 26, pulses of negative pressure or rarefaction are delivered by the piston to the adjacent end of the liquid column in pipe 10. These similarly travel the length of the liquid column in pipe 10, are reflected, and returned. The traveling waves of compression and rarefaction interfere with one another in a manner well understood by those skilled in the art of sonics to produce regions of maximum pressure variation (pressure antinodes) at the two regions P and P', while at the midway point V (velocity antinode), the pressure waves cancel one another, and the liquid body oscillates back and forth, as indicated by the double-headed arrow. It will be understood that the pressure variation amplitude is maximized at P and P, and tapers off to a minimum at V. It will also be understood that the pressure variation cycle is superimposed on the mean pressure level of the crude in the system.

In the operation of the system, crude oil at super-atmospheric pressure from one or more Well heads is introduced via intake line 11, filling the pipe 10 up to the end caps 14 and 15, and the piston 26 is then oscillated at a resonant frequency of the pipe 10. A sonic standing Wave isthereupon established in the liquid column in the pipe 10, as described above, with maximum pressure variation zones at P and P.

It will be understood that the crude arriving via the intake pipe 11, and held within the sonic pipe 10, is under a gas pressure considerably above atmospheric pressure, and is assumed to contain a large amount of gas in solution. The pressure waves created in the two half portions of the sonic pipe (from P to V, and from P to V) alternately raise and then lower the pressure on the crude. In other words, the crude is maintained at an elevated, i.e., super-atmospheric, mean pressure, on which is superimposed a fluctuating pressure above and below mean pressure, of amplitude dependent upon the stroke of the oscillating piston 26. As stated above, the amplitude of this pressure fluctuation, above and below mean pressure, is maximized at the regions P and P, and tapers to a minimum, or zero, at V.

In general, for any given stroke amplitude of the piston 26, somewhat diflerent conditions will prevail for different gas fractions, and the diflerent fractions will be released from solution selectively, or to different extents and different rates. The rate of release of a given fraction will also depend upon the extent to which the fluctuating pressure amplitude reduces the pressure to or below cavitation pressure for that fraction.

The fluctuating pressure amplitude has been explained as being at a maximum at P and P and at a minimum at V. Now, it will be seen that, for any gas fraction, and assuming a pressure swing at P and P more than sufficient to attain cavitation conditions at those points during the negative halt cycles of the wave, the greater the amplitude of the pressure swing, the greater will be the distance along the liquid column, from P or P toward V, that low-pressure cavitation conditions will be cyclically established and the greater, therefore, will be the volume of the contained crude from which gas bubbles will be rapidly evolved. It will thus be evident that diflferent release rates may be established for different fractions by adjustment of the pressure fluctuation amplitude.

On each negative pressure half cycle (negative relative to the mean pressure level), gas in solution in the crude is released, particularly when cavitation pressure levels are approached or passed for given gas fractions. The gas bubble generation may be at a maximum in the pressure antinode regions P and P, though will generally occur for a distance towards the region V. The gas bubbles so released beyond the regions P and P tend to rise to those regions; and the gas collected in the regions P and P is continuously delivered at the elevated mean pressure of the system via the discharge pipes 16 and 17. By thus continuously drawing off the released gas, it is prevented from going back into solution in the crude.

FIG. 2 shows a modified embodiment, comprising a cylinder 40 containing a reciprocating wave-generating piston 41, and filled with an exponentially tapering cylinder head 42, to the small end of which is connected a gas delivery pipe 43. Crude oil intake and discharge pipes 44 and 45, respectively, connect into head 42, as shown.

The head 42 forms an exponentially tapering pressure chamber 45 for the crude, with a gas delivery pipe leading from the top.

In operation, gas-containing crude oil under pressure is circulated through pressure chamber 46, in at 44 and out at 45. The piston 41 is oscillated at such a sonic wave frequency as will generate sound waves that will travel through the crude oil from the large to the small end of the horn-shaped chamber.

The oscillation frequency of the piston is made such relative to the taper ratio of the horn to assure transmission of a sound wave delivered by the piston from the mouth to the neck of the horn, as will be readily understood by those skilled in the art.

Acoustic impedance, which is proportional to the quotient of sound wave pressure and particle velocity in the wave transmission path, is relatively low at the mouth of a horn, and relatively high at the neck, with a continuous transition therebetween. In other words, at the mouth of the horn, there is superimposed on the mean pressure of thecrude flowing through the horn, a fluctuating sonic wave pressure cycle of relatively low amplitude; md at the neck region, there is superimposed on the mean pressure, a sonic wave pressure cycle of relatively high amplitude. This high amplitude pressure cycle, within the high impedance neck region of the horn, is suitable for degassing the crude oil, according to principles discussed in connection with FIG. 1. Suflice it to say that the piston 41, operating against the pressurized crude oil, generates a sonic pressure wave which, on its negative half cycles, reduces the pressure sutficiently to release gas from the crude, which gas then rises in the horn-shaped chamber and is delivered from the top, still at elevated pressure. The sonic wave generated by the piston preferably operates in a range such as to establish cavitation, as described in connection with FIG. 1.

FIG. 3 shows a modification of the invention according to which the wave system is established primarily in a boundary wall of the treatment chamber, rather than primarily through the crude oil. Numeral 5t) designates a preferably slightly tilted, elastically gyratory pipe, composed of a good elastic material, as steel. A crude oil inlet 51 opens into one end of pipe 50, and an outlet 52 for the degassed crude leads from the opposite end of pipe 59. Leading upwards from the high end of pipe 50 is a gas discharge outlet 53. Inlet 51, outlet 52, and outlet 53 are connected by flexible couplings 54 to pipe lines 55, 56, and 57, respectively. The pipe 59 is mounted a quarter of its length from each end through flexible rubber mounts 58 from a suitable base 59.

A gyratory wave generator 64 is mounted on one end of pipe 50, and the opposite end of pipe 5% is closed by an end plate 61.

Generator 60 comprises a housing 61 secured to the end of pipe 59, and provided in its end with an axial inlet 62 for compressed air. Inside housing 60 are, in order, an air distributor 63, a spacer plate 64, a plate 65 formed with a circular roller chamber 66, a spacer plate 67, and an air discharge annulus 68. Compressed air from inlet 62 passes through passages 69 in distributor 63, ports 7%) in spacer 64, and passages 71 in chamber plate 65. Thence, the air passes through slots 72 cut in opposite edges of plate 65 and leading tangentially into chamber 66. Within chamber 66 is an inertia roller 74, which is driven by the tangential air jets from slots 72 to spin or roll about the periphery of the chamber. The Spent air is discharged from chamber 66 via ports 75 in spacer 71, central opening in annulus 68, and radial discharge passages 77.

The spinning inertia roller exerts a gyratory force on the housing of generator 60 and therefore on the end of pipe 5% In response to this force, the end portion of the pipe 59 bends elastically and moves bodily in a circular path. That is, each point on the end of the pipe describes a small circle in a transverse plane. This elastic gyratory deformation of the pipe (which is a form of transverse or lateral harmonic vibration, being the resultant of two perpendicular transverse linear harmonic vibrations in quadrature), is propagated lengthwise of the pipe, and reflected from the ends thereof; and when the air pressure is such as to drive the roller about its chamber at a number of revolutions per second which is in the region of a resonant frequency for the pipe 50 for lateral vibration, the pipe is set into strong gyratory standing wave vibration. The fundamental standing wave pattern is one wavelength, with a velocity antinode region of maximum gyration amplitude at each end of the pipe 51) and at its midpoint; and a pressure or stress antinode (region of minimum or zero gyration amplitude) at approximately one-fourth distance in from each end. It will be seen that the support points for the pipe 50 have been located at the velocity nodes.

Wave propagation and standing waves of this character have been disclosed in my earlier applications as fol- 6 lows: Method and Apparatus for Generating and Transmitting Sonic Vibrations, Ser. No. 313,175, filed October 4, 1952, and Apparatus for Generating and Transmitting Sonic Vibrations, Ser. No. 484,627, filed January 28, 1955, now both abandoned.

In operation, the crude oil, under pressure, is circulated in through inlet 51, travels the length of pipe 50, and the degassed crude is delivered via outlet 52. The action of the gyrating pipe on the contained crude in contact with its inside surfaces is to subject the crude to alternating compressions and rarefactions with reference to the mean pressure of the crude inside the pipe. The pressure rarefactions, both down to, and below the level of cavitation, have degassing influences on the crude of the same nature, as discussed in connection with earlier described forms of the invention. The released gas migrates to the elevated end of the pipe 59, and is taken off, at elevated mean pressure, via outlet 53.

FIG. 5 shows a modification similar in many respects to that of FIGS. 3 and 4. A gyratory elastic pipe 70, corresponding to pipe 543 of FIG. 3, is driven to undergo a gyratory standing Wave by gyra-tory generator 71, which may be of the type of generator 60 of FIG. 3. Pipe 79 may be externally or internally supported by rubber mounts (not shown) at points approximately one quarter of its length from each end, at the locations of the velocity nodes.

A treatment cylinder 74 surrounds and is packed to pipe 70 by resilient seals 75, also located at the velocity nodes. A crude oil inlet is shown at 76, a degassed crude outlet at 77, and a gas outlet at 78. The cylinder 74 is preferably slightly tilted, so that the gas outlet 78 is at the high end. A perforate sleeve 79 surrounds and is annularly spaced outside pipe 79 between the end Walls of cylinder 74.

In operation, flow of crude oil through the treatment cylinder is established at such a rate as, prefer-ably, to maintain a liquid level just slightly higher than the top side of sleeve 79. The gyratory pipe 70, acting on the surrounding crude oil, subjects the crude to compressions and rarefactions relative to the elevated mean pressure maintained inside the system. The result of the cyclic ne ative pressure excursions is to degas the crude, in the manner described in connection with the earlier embodiments of the invention. In the case of FIG. 5, 1 prefer to maintain the liquid level in the cylinder 74 at only a short distance over the pipe 70, in order to limit the amplitude of the compression waves that can be superimposed on the mean pressure at which the crude oil is held. It will be seen that, under some circumstances, a negative pressure pulse generated by the bottom side of the pipe 70 might be, at least in part, cancelled by a positive pressure pulse simultaneously generated by the top side of the pipe. If, however, only a small quantity of liquid overlies the top side of the pipe, a strong positive pressure pulse cannot be generated therein, and no material negative pulse neutralization can occur.

The purpose of the perforated sleeve 79 is to retard separated gas from going back into solution.

The thin layer of liquid above the sleeve may become relatively gas saturated. This saturated layer of liquid has only limited gas communication with the liquid inside the sleeve, and gas is thus slowed from going back into solution in the crude inside the pipe. Moreover, the saturated layer of liquid above the pipe acts as a barrier to stop or greatly reduce the separated gas from going back into solution.

The invention has now been illustrated in several illustrative forms. It is to be understood that these are merely illustrative, and that various further changes in design, structure and arrangement may be made Without departing from the spirit and scope of the invention as defined in the appended claim.

I claim:

The method of treating underground-pressurized crude oil produced from petroleum wells and held at superatmospheric pressure to separate therefrom components which are in liquid form at said superatmospheric pressure but normally in a gaseous phase at atmospheric pressure, without depletion of said superatmospheric pressure, that comprises: placing said pressurized crude oil in a pressuretight container, maintaining the mean pressure of the crude oil within said container at the superatmospheric pressure level, and superimposing on said mean pressure a standing sound wave which cyclically lowers the pressure on the crude oil below said superatrnospheric pressure 15 level in the region of a pressure antinode of said sound 5 said crude oil and on the separated gas phase components.

References Cited in the file of this patent UNITED STATES PATENTS 10 1,554,835 Barrett Sept. 22, 1925 2,190,104 McCoy Feb. 13, 1940 2,363,247 Holder Nov. 21, 1944 2,620,894 Peterson et al Dec. 9, 1952 2,652,000 Woolsey Sept. 15, 1953 FOREIGN PATENTS 458,893 Great Britain Dec. 29, 1936 

